Optical Add-Drop Multiplexers (OADM) is an essential component of the Dense Wavelength Division Multiplexer (DWDM) for applying on the node of internet and adding/dropping the wavelength so as to simplify the networks.
The increasing sophistication of a rapid expansion of network users demands for very high-speed networks with higher bandwidth and higher speed of router. Through the introducing diversity of service in network, the network shall have higher elastic scheduling. The new generation of network not only has higher transmission speed, longer transmission distance, but also capacity for various signals and dynamic bandwidth configuration. Based on such concept, in combination with DWDM (dense wavelength division multiplexing), tunable technology, and integrated technology, a reliable, stable network is provided. In order to deal with the increased number of wavelength on each optic fiber of the DWDM, the design of the OADM is getting complicated for enlarging the bandwidth. Therefore, the demand and practicability of tunable OADM is higher day after day.
So far, a lot of technology related to Optical Add/Drop Multiplexer has been published such as the optical add/drop multiplexer composed by the AWG (Arrayed waveguide and grating) and optical switch, bragg grating-assisted Mach-Zehnder Interferometer-based OADM made of or Mach-Zehnder Interferometer and fiber grating (refer to the paper: T. Erdogan, T. A. Strasser, M. A. Milbrodt, E. J. Laskowski, C. H. Henry, G. E. Kohnke, “Integrated-optical Mach-Zehnder add-drop filter fabricated by a using UV-induced grating exposure,” Appl. Opt., Vol. 36, pp. 7838–7845, 1997), or Acoustic-Optic Tunable Filter OADM, Fiber Bragg grating OADM (refer to the paper: A. S. Kewitsch, G. A. Rakuljic, P. A. Willems, and A. Yariv, “All-fiber zero-insertion-loss add-drop filter for wavelength-division multiplexing,” Opt. Lett., Vol. 23, No. 2, pp. 106–108, January 1998). The tunable OADM (refer to the paper: P. Tang, O. Eknoyan, and H. F. Taylor, “Rapidly tunable optical add-drop multiplexer (OADM) using a static-strain-induced grating in LiNbO3,” J. Lightwave Technol., Vol. 21, No. 1, January 2003.) available on the market today is composed of various components and circulator thus the structure is complicated, the volume of the module or system is quite large and the cost is high. The fiber grating OADM uses the elasticity or temperature change to tune the period of fiber grating while the adjust time is long and the modulation speed is slow. The Acoustic-Optic Tunable Filter (AOTF) has low sensitivity to polarization. Although electro-optical tunable filter (EOTF) can improve the sensitivity problem of AOTF, both of them have the problem of broad bandwidth and wavelength that is difficult to overcome.